Achromatic Prism Layout for HMD Display Compound Angles
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Solution Overview
Problem
The configuration of display, illumination, and projection optics in head-mounted devices is complicated, leading to challenges in positioning the image output relative to the display and optics, particularly in accommodating compound angles and minimizing chromatic aberrations.
Innovation Solution
The use of an achromatic prism to shift the exit beam angle and decouple the position of the display and optics, allowing for a flexible design that accommodates compound angles and reduces chromatic aberrations, with materials and configurations tailored to specific head-mounted device form factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the display and optics are positioned in a standard configuration, then the system is simple to design, but the image output position cannot be decoupled from the display position, making it difficult to fit into compact form factors
Solution Approach 1:
An achromatic prism is introduced as an intermediary optical element between the display/optics and the waveguide. This prism decouples the position of the display engine from the image output position, enabling the system to fit into compact form factors while maintaining proper optical alignment. The prism acts as a mediator that redirects light paths without introducing chromatic aberrations.
2Manufacturing precision
If standard projection optics are used, then the system is easy to manufacture, but chromatic aberrations cannot be minimized
Solution Approach 1:
The achromatic prism is constructed from composite optical materials with different dispersion properties. By combining materials with complementary chromatic characteristics, the prism cancels out chromatic aberrations while maintaining manufacturing feasibility. This composite material approach allows precise control over color fidelity without requiring overly complex optical designs.
3Temperature
If the light enters the waveguide at an angle, then the image output can be displaced from the optics position, but the optical configuration becomes more complicated
Solution Approach 1:
The optical system is segmented into distinct functional modules: the display engine, the achromatic prism, and the waveguide. This segmentation allows each component to be optimized independently for its specific function. The prism handles angular redirection and position decoupling, while the waveguide focuses on image delivery, simplifying the overall system architecture despite the angled light path.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the display system to fit into a glasses form factor while maintaining good optical performance and accommodating various head-mounted device configurations, effectively managing compound angles and chromatic aberrations.
Implementation Method 1
A prism is used to shift the exit beam angle and thus the position of an output image
Implementation Method 2
an achromatic prism is used to avoid chromatic aberrations
Data Source
AI summary
A display system for a head mounted device (HMD) including a lens comprising a display area on the lens of the HMD, the lens having a base angle and a pantoscopic tilt, a display engine and optics, and a prism to redirect output from the optics to the display area on the lens of the HMD, accounting for the base angle and the pantoscopic tilt.